rigify face rigging isues
It looks like it would probably be the last bone in the chain coming up from the chin. It looks like that bone ends in the middle of the mouth which would make the automatic weights consider the mouth to be part of the chin and the face would just look elongated when rotating the jaw.
I highly recommend you to learn weight painting though since an issue like that would be very easy to detect if you would scroll through the groups.
Also, I would recommend you to use video for reference while placing the bones and try to replicate the placement when trying out new rigify rigs since they can be very delicate.